| Recently, our country great imports clean energy-LNG(Liquefied NaturalGas), and the main equipment of LNG received station is ultra-low temperatureLNG tank which made by06Ni9steel(equated to foreign9%Ni steel). The paperis focusing on development research of06Ni9steel which used for ultra-lowtemperature LNG tankThe developing and research team consisted of Shanxi Taigang StainlessSteel Co., LTD and Taiyuan University of Technology. Based on national project,the team had developed laboratory research and industrialized production. Theteam successfully solved tens of technical problems of06Ni9steel, for example,ultra-pure metallurgy, uniform and high quality casting, excellent surface quality,excellent matching of mechanical property, remanence controlling and weldingtechnical of steel, precast processing molding and surface protection treatmentby technical route of hot metal pretreatment, BOF, LF, RH, continuous casting,rolling, modified treatment and precast processing molding. The team formed asuite of production and application technology of06Ni9steel. The teamresearched the comprehensive mechanical properties, especially AKv at-196℃.The welding property of steel was better than foreign production. Properties fully meet strict specification of building national large-size ultra-lowtemperature LNG tank. Eight tanks were built and operated safely by06Ni9steel which displaced foreign steel. The main research achievements of thispaper were as follow.1）The research first developed the ultra-pure smelting technology ofalloyed steel with high nickel content in domestic. The industrial process of06Ni9steel which [P]＋[S]＋[H]＋[N]＋[O]≤100ppm and very extra-lowcontent of low-melting elements can be stabilizing controlled. All technologieslaid a scientific foundation in excellent mechanical property and ultra-lowtemperature toughness of steel.2）The research integrated and innovated the process technology of hotmetal pretreatment+BOF+LF+RH+continuous casting. It successfully solved thehigh crack sensitivity of06Ni9steel in continuous casting process. The researchfirst developed HLH (High casting speed, Low superheat, High temperaturestraightening) continuous casting technology of06Ni9steel in domestic. Theproblem of controlling the ultra-low phosphor (P≤0.005%in specification) hadbeen solved. In domestic, TISCO had been the first company which can produce06Ni9casting slab with these advantages, for example, high purity, highuniformity, high density, less internal defect, bright surface and so on. AndTISCO had produced the same properties plate which compared with foreigncompanies (ArcelorMittal, JFE).3）TISCO had developed the specific oxidation protection technology of 06Ni9steel slab under high temperature heating independently by guarding theslab surface (special coating for06Ni9steel) and controlled rolling technology.It successfully solved the problem of removing iron scale during rolling of steelwith high nickel.4）06Ni9plate was produced with good surface, lower thickness toleranceand excellent plate shape by controlling rolling and plate shape of heat treatmenttechnology. Meanwhile, the plate that supplied to customers was handling bypre-manufacturing and forming type. It elongated chain (the same as deepprocessing product) and increased the added value of product.5）The research first developed the low temperature controlling rolling andQT technology for06Ni9steel producing in domestic. The products hadstabilized quality and excellent over-all properties. Especially, excellent lowtemperature fracture toughness property and bending property were better thatforeign product with the same class. It was important to guarantee lowtemperature project operation safely and steady.6）The research developed the whole advanced producing technology of06Ni9steel. TISCO become the first company which can produce plate and usefor the national major project. Several super-huge LNG tanks were built byTISCO’s plate. The research made all materials used for inner tank can beproduced in domestic. It terminated that the key low temperature materials mustbe imported in national energy field.7）The research grasped the strengthening-toughening mechanism of06Ni9 steel. It analyzed and discussed the microstructure, fine fabric, especially how toforming the reversed austenite in06Ni9steel by test. The research gained thetransformation mechanism of forming reversed austenite during temper. Itconfirmed that the reversed austenite played an important role in lowtemperature toughness of06Ni9steel.8）By foreign exclusive stick electrode, the research carried out the basicproperty test of welding joint of06Ni9steel with different welding process andheat treatment after welding. The welding property of steel was evaluated byhighest hardness method in HAZ and crack sensitivity test with groove welding.The results showed that the developed06Ni9steel was not need pre-heat beforewelding, and the cold crack sensitivity was low. The welding gists were asfollow, multiple process, little heat input and interlaminar temperaturecontrolling. All these strategies aimed to decrease the influence for HAZ ofwelding joint.9）The research analyzed the06Ni9steel used for several huge LNG tank(10000m3,30000m3,80000m3,160000m3,). The results showed that the purityof steel was better than foreign steel, especially low-smelting elements.Compared with foreign steel, it made larger advantages in low temperaturetoughness, welding and ageing sensitivity.06Ni9steel fully meet requirementsof constructing.Several patents and exclusive processing technology were developed forthe key low temperature material used for LNG tanks by this research. The research supplied study basic and technology protection for producing06Ni9steel with excellent and steady low temperature toughness property. As the firstdeveloped key material for national grave project,06Ni9steel passed theidentification of experts organized by Shanxi province science office. Theidentification result showed that the substance quality of06Ni9steel reached theinternational advanced level. The research steel had been successfully used forsuper-huge LNG tanks. It terminated that the key material in need must beimported. The research filled-up the blank in domestic. There were veryobviously economic benefits and social benefitsThe research materials had been granted4patents and published14articles.The research project won the first progress prize in scientific and collectivetechnology of metallurgy. |
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